Dose measurements with the Pille-ISS thermoluminescent dosimeter system during extravehicular activities (2004-2022)

Abstract

One of the most problematic goals for radiation safety during spaceflight is an assessment of additional doses received by astronauts during extravehicular activity (EVA). The Pille-ISS thermoluminescent dosimeter developed by the predecessor of the Hungarian Research Network (HUN-REN) Centre for Energy Research (Budapest, Hungary) is designed for the routine dose measurements not only inside the spacecraft compartments, but also for personal dosimetric control for EVA. During almost two decades of the International Space Station (ISS) operation, the unique set of 131 EVA doses were recorded in different conditions, such as: solar activity, ISS trajectory along the South Atlantic Anomaly (SAA), and shielding conditions provided by two kinds of spacesuits: the Extravehicular Mobility Unit (EMU) and Orlan.

The EVA dose rates during the normal scenario (without SAA crossing during EVA) are: 26 $\mu$Gy/h on average, with maximum value of 118 $\mu$Gy/h for the EMU spacesuit; and 103 $\mu$Gy/h on average, with maximum value of 255 $\mu$Gy/h for the Orlan spacesuit. However, the corresponding EVA dose can increase by about 33% on average regardless the spacesuit type, depending on time spent in SAA. The worst case mean EVA dose is equivalent to $\sim$ 7 days inside the ISS with 2.423 mGy. In general, the possible additional radiation risk due to the EVA is small in comparison with typical half-year mission onboard the ISS.

The long-term experience of EVA dose assessments with Pille-ISS dosimeter shows that in some cases the skin dose can be underestimated due to the excessive shielding of the standard Pille-ISS dosimeter. To solve this problem, the modified Pille-ISS dosimeters with significantly reduced shielding are developed and involved onboard the ISS for the dose measurements starting from 2023.